temperature control

[tomsm44]

I recently built a small propane forge to use for heat treating now and eventually to use for forging.  It is made of from 8 fire bricks and is held together by a frame I built out of angle held together by all thread.  Welded would have looked better, but I'm not a welder.  Also, I can back the nuts off and replace the bricks easily if needed, which I plan to do because I used hard brick initially bacause I had a cheap source nearby for it.  I plan to replace it with soft brick bacause the hard brick I got is only good to 1750 degrees.  It uses a ventouri burner that I also built.  I have heat treated a few knives with it and it will heat an 1/8" thick knife to non magnetic in just a couple of minutes.  What I want to know is what is the easiest and cheapest way to monitor the temparature inside the forge.  I'm not interested in it controlling the forge, just reading temperature.  I will adjust the regulator manually to get the desired temp.  I've read instructions for using a digital temparature controller with a thermocoupler and a solenoid valve and I could leave out the solenoid valve and use this setup simply as a thermometer, but it would cost me around $250.  Do any of you guys know of a cheaper setup that would read temp up to at least 2000deg, preferably 2500 to make sure I don't accidentally over range it?

Thanks,
Matt Toms

[tomsm44]

Another thing, I know a lot of guys use color to judge the temparature of steel when forging and heat treating.  If any of you know of a link to some good information, preferably with pictures or video, I would greatly appreaciate that as well.

[Lin Rhea]

Unless you can set the forge at a top end temperature, it wont do much good to know what the temperature is. You will wind up using color anyway. Even if you set it, it will be that temperature right where the thermocouple is. In other words, a forge has hotter and less hot places throughout.

In my opinion, if you are going to use a forge to heat treat, you may as well get a good magnet and calibrate your eye from that.

[tomsm44]

Thanks Lin, that makes a lot of sense.  That'll save me some money also.

[gables]

I have a thermocouple in my forge and it sometimes allows me some control- like when I use a thick stainless pipe in my forge for heat treating. I run the thermocouple into the tube.

Most helpful, however, has been a laser thermometer that goes to 1832 degree F. You can heat up steel and pull it out of forge, put laser on it and watch the temperature drop and watch the color shifts at the same time. I use this laser all the time to check things before grabbing, temp of oil and also for some forge heat treating. It took a while to find the right model that at least went to 1600 degrees.

  http://www.testersandtools.com/Extech-42542-IR-Laser-Thermometer.php

[Lin Rhea]

Gabe makes a good point about the pipe. That would make the thermocouple a worthwhile tool in that case. Very good observation.

[tomsm44]

Thanks Gabe.  I haven't tried using a piece of pipe for heat treating, but I've read a little about it.  I had thought of the laser thermometers, but I had never seen one with a high enough range.  The ones we use in the natural gas industry to check temperatures on compressor valves, cylinders, etc. only go to around 800-1000 deg.

[gables]

One last point is that I support the end of my thermocouple up with a small piece of fire brick to keep it off the pipe. I then lean my knife right against this brick piece so the thermocouple is beside the knife. I put the blade spine down. I use my shutoff valve and throttle the forge to keep the temp +\\- 5 degrees. I use a timer and double check my temps with the laser thermometer for soak times. All in all I spent $325 for my system. It has served well while I save for an oven but I am lucky to have a good friend with an oven for more complex HT.

[tomsm44]

That's why I'm sticking with relatively simple heat treat steels; 1095 & 1084 mainly. Almost set up to start forging and want to try some "big" knives.  I may try some 5160 as that seems to be a good choice for a tough, working Bowie.  Or so I hear at least.  Thanks for the info guys.